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This invention relates to a liquid delivery system and is especially suitable for use as part of an infusion pump system designed to deliver parenteral and enteral fluids, as well as whole blood or red blood cell components, using a wide variety of standard intravenous administration sets and fluid containers.
One conventional type of infusion pump system employs a peristaltic pump in conjunction with an intravenous administration set. The set consists of flexible thermoplastic tubing through which fluid flows from a suspended container, such as a flexible bag or rigid bottle, to a patient""s indwelling vein access device, such as a needle or cannula inserted into the patient. A length of the administration set tubing between the fluid container and the patient is mounted in the peristaltic pump which sequentially squeezes adjacent sections of the tubing so as to pump the fluid via a peristaltic action along the tubing into the patient.
Liquid medical products which are intended to be administered intravenously are typically stored in a central location in a hospital or other medical facility. Some such liquid products are typically stored in a refrigerator or cooler to preserve the product efficacy or to extend shelf life.
When a refrigerated liquid product is removed from storage and administered to a patient, the bulk of the liquid within the dispensing container or package typically remains relatively cold during the administration of the liquid patient. The administration tubing set through which the cold liquid flows also becomes cooler.
Conventional administration set tubing is molded from a polyvinyl chloride polymer, and the resiliency of this material decreases substantially with decreasing temperature. On the other hand, when the polyvinyl chloride polymer tubing is at normal room temperature, the tubing is much more flexible and resilient.
A peristaltic pump control system can be simply designed to provide a selected flow rate when operating at a constant speed with the tubing at a particular temperature (e.g., normal room temperature). When such a pump is operated on tubing at normal room temperature to squeeze and release a section of the tubing, the deformed tubing recovers to its original cross-sectional configuration relatively quickly. Thus, before that same section of tubing is subsequently squeezed again by the peristaltic pump, that section of tubing will be filled with substantially the same volume of liquid as was contained in the tubing during the prior pump stroke. Hence, a constant pump stroke rate relative to the section of tubing results in the pumping of constant flow rate of liquid through that section of tubing if the tubing temperature does not change.
However, if the temperature of the tubing decreases, the tubing becomes stiffer and less resilient. This can change the pumping characteristics. Consider the situation if a refrigerated, cold liquid is pumped through the tubing. When the peristaltic pump acts on a section of the cold tubing to first squeeze or deform the tubing into a closed configuration and then releases the tubing, the cold tubing will not recover to its original cross-sectional configuration as quickly as it would if it was at room temperature. Indeed, the tubing may not recover to its original cross-sectional configuration by the time the peristaltic pump again cycles to squeeze closed that same section of tubing. If the cold tubing has only recovered, say, about 75% of its full open cross-sectional configuration before being squeezed again by the peristaltic pump, then that section of tubing would contain substantially less liquid than if that tubing section had fully recovered to its original cross-sectional configuration prior to being subsequently squeezed by the pump.
Typically, peristaltic pumps are intended to supply a liquid through the administration set tubing at an adjustable, but constant rate. The rate may be adjusted to a selected rate over a range of rates. If a patient is supposed to receive, say, 10 milliliters per hour of liquid, then the peristaltic pump can be set to provide that flow rate based upon a pump operating speed which has been determined by the pump manufacturer for tubing at a constant temperature, typically a normal room temperature. If the temperature of the tubing differs from that used by the pump manufacturer in establishing the pump flow control system relationship between pump operating speed and flow rate, then the control system will not provide the desired flow rate when the tubing is at a higher or lower temperature.
Accordingly, it would be desirable to provide an improved system for regulating the fluid flow through a peristaltic pump. Such an improved system should accommodate variations in temperature, including variations in the temperature of the liquid product being administered to the patient as well as variations in ambient temperature.
Preferably, temperature sensing instrumentation used in such an improved system should also be protected from electrostatic discharge so as to eliminate, or at least minimize, the potential for damage to such sensors.
The present invention provides an improved system which can accommodate designs that have the above-discussed benefits and features. The system is convenient to use and is cost-effective with respect to its manufacture and operation. The system is especially suitable for use in a peristaltic pump. However, the system is applicable to other types of pumps wherein fluid is pumped through tubing and the fluid temperature cannot be directly sensed.
The system is easily operated and can be used with a wide variety of standard administration sets and fluid containers. The system is designed to meet the growing demand for hospital-wide standardization, as well as alternate-site, in-home healthcare standardization.
The improved system of the present invention accommodates safe delivery of fluids to a patient. The system is convenient to operate and is easy to set up.
One aspect of the present invention relates to an improvement in a peristaltic pump for pumping fluid through tubing. The improvement comprises a temperature sensor adjacent the tubing for sensing the temperature of the tubing. If the tubing is cooled because a refrigerated liquid is being pumped through the tubing, then the resulting decrease in pumping flow rate (owing to a slower recovery of the deformed tubing cross section to its original configuration) can be correlated to an increased pump operating speed necessary to maintain the flow at the desired rate substantially independent of temperature variations.
According to another aspect of the present invention, a process is provided for regulating the fluid flow through flexible tubing in a peristaltic pump where a section or length of the tubing which has been peristaltically deformed recovers to its original cross-sectional configuration at a rate dependent upon the fluid temperature. The process includes the step of sensing the temperature at a location on a heat transfer path which includes a portion of the tubing inside the pump. Preferably, the heat transfer path extends from the tubing to a temperature sensor. In the preferred embodiment, the heat transfer path includes interposed materials, such as an electrostatic discharge protection material and an epoxy material bonding the electrostatic discharge protection material to a temperature sensor.
The process includes the further step of sensing ambient temperature inside the pump at a location spaced from the tubing and thermally insulated from the heat transfer path. The process further includes the step of adjusting the pump operating speed as a function of the two sensed temperatures.
According to yet a further aspect of the invention, the process includes disposing a first temperature sensor in the peristaltic pump against the surface of an interposed thermally conductive structure which is located between, and in contact with, the exterior surface of the tubing and the first temperature sensor. The temperature Ts of the surface of the thermally conductive structure is determined by the first temperature sensor.
A second temperature sensor is disposed in the pump at a location spaced from the tubing and interposed thermally conductive structure. The ambient temperature Ta is determined by the second temperature sensor.
Next, the temperature Tf of the fluid at the interior surface of the tubing is calculated according to the formula       T    f    =                    bT        a            -              T        s                    (              b        -        1            )      
where b is an empirically determined constant equal to (Tfxe2x88x92Ts)/(Tfxe2x88x92Ta) calculated from a measured value of the temperature Ts when both temperatures Tf and Ta are fixed at selected values.
Subsequently, the process operates the pump at a variable speed as a function of the calculated temperature Tf.
According to yet another aspect of the invention, the process includes disposing one side of a thermally conductive electrical insulator against the exterior surface of the tubing in the pump. A first temperature sensor is bonded to the other side of the electrical insulator with an interposed layer of thermally conductive bonding material so as to define a heat transfer path from the tubing to the first temperature sensor. The temperature Ts at the interface between the bonding material and the first temperature sensor is determined by the first temperature sensor.
A second temperature sensor is disposed in the pump at a location thermally isolated from the heat transfer path. The second temperature sensor is bonded to one side of a thermally conductive electrical insulator with an interposed layer of thermally conductive bonding material. The ambient temperature Ta is determined by the second temperature sensor.
The process further involves periodically calculating the temperature Tf of the fluid at the interior surface of the tubing according to the formula       T    f    =                    bT        a            -              T        s                    (              b        -        1            )      
where b is an empirically predetermined constant equal to (Tfxe2x88x92Ts)/(Tfxe2x88x92Ta) calculated from a measured value of the temperature Ts. where both temperature Tf and Ta are fixed at selected values.
Subsequently, the process varies the pump operating speed inversely with, and as a function of, changes in the calculated temperature Tf.
According to yet another aspect of the present invention, a system is provided for indirectly sensing the temperature of fluid flowing through flexible tubing in a pump. The system includes a first thermally conductive electrical insulator that has oppositely facing first and second surfaces and that is mounted in the pump with the first surface in contact with the exterior surface of the tubing.
The system includes a first temperature sensor and a first thermally conductive bonding material bonding the first temperature sensor to the second surface of the electrical insulator.
The system includes a first electrically and thermally insulating material extending from the bonding material to encapsulate the first temperature sensor.
The system also includes a second thermally conductive electrical insulator that (1) is spaced from the tubing, (2) has oppositely facing first and second surfaces, and (3) is mounted in the pump with the first surface exposed in the pump to the pump ambient temperature.
A second temperature sensor is included in the system, and a second thermally conductive bonding material bonds the second temperature sensor to the second surface of the second electrical insulator.
The system includes a second electrically and thermally insulating material extending from the second thermally conductive bonding material to encapsulate the second temperature sensor.
Yet a further aspect of the invention includes a temperature sensing system of the type described above together with a special housing for being mounted in the pump. The housing includes (1) a first receiving block that defines a first aperture, and (2) a second receiving block that is spaced from the first receiving block and defines a second aperture.
The first thermally conductive electrical insulator includes a first plate defining oppositely facing first and second surfaces. The first plate is mounted in a first receiving block at the end of the first aperture to occlude the first aperture with the first surface of the first plate facing out of the first aperture and with the oppositely facing second surface of the first plate facing into the first aperture.
The first temperature sensor is disposed in the first aperture. The first thermally conductive bonding material bonds the first temperature sensor to the second surface of the first plate.
The second thermally conductive electrical insulator includes a second plate defining oppositely first and second surfaces. The second plate is mounted in the second receiving block at one end of the second aperture to occlude the second aperture with the first surface of the second plate facing out of the second aperture and with the oppositely facing second surface of the second plate facing into the second aperture.
The second temperature sensor is disposed in the second aperture. The second thermally conductive bonding material bonds the second temperature sensor to the second surface of the second plate.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention, from the claims, and from the accompanying drawings.